Mastication (Chewing)

Dr. Mohammed Alzoghaibi

Mastication (Chewing) Teeth organization• Anterior teeth (incisors) for cutting• Posterior teeth (molars) for grinding

Chewing muscles are innervated by CN V Taste center (Hypothalamus) rhythmical

chewing movementso Chewing reflex & stretch reflex

Mastication (Chewing)

Functions:

1. To lubricate the bolus with salivary secretion2. To breakdown the bolus to small particles

3. To begin digestion of carbohydrate (amylase)

SALIVARY SECRETON

Anatomy Parotid glands Submandibular (submaxillary) glands Sublingual glands Smaller glands in mucosa of tongue, palate,

etc.

Composition of Saliva

Aqueous fluids Water, ions and enzymes Parotid, submaxillary and sublingual glands

Mucus secretion (mucin) Submaxillary and sublingual glands

Composition of Saliva Aqueous Fluids H2O, K, HCO3, Na, Cl, -amylase, lingual lipase,

IgA, kallikrein, muramidase (lyses muramic acid of Staphylococcus), lactoferrin and EGF

Hypotonic Solution Ions Na, K, CI, HCO3: (concentrations altered with altered flow

rates) At low flow rate High K and HCO3

Low Na and CI−

Composition of Saliva

Enzymes -amylase, parotid glands • cleaves -1 ,4-glycosidic bonds • pH optimum of 7 • inactivated @ pH 4 but continues to work for sometime

in unmixed food in orad portion of stomach

Lingual lipase • hydrolyzes lipids • continues working into duodenum

Composition of Saliva

Enzymes (Cont) Kallikrein (protease, acinar cells)• Catalyzes production of bradykinin from -

globulin• Increase local blood flow

Water (0.5 L saliva/day)

Secretory Unit (salivon) The basic unit “salivon” consists of:Acinus -initial secretory process Intercalated duct -initial portion of duct Striated duct -modification of secretory

product Myoepithelial cells surround acinus and intercalated duct contraction moves saliva, prevents

development of back pressure

Characteristics of Saliva and Flow Rate

Daily secretion = 800-1500 mL PH = 6-7

Functions of Saliva

moistens food begins digestion adjusts salt appetite Contains factory that destroy bacteria Thiocyanate ions and antibodies lactoferrin which chelates iron necessary for bacterial growth Lysozyme: i. active against bacterial wallsii. Helps thiocyanate in entering bacterial wall and where they become

bactericidal

Control of Secretion

Unique aspects of control of salivary secretion secretion rate depends entirely on neural

control -ANS both Parasympathetic and Sympathetic lead to

increase secretion Composition modified by Aldosterone increases Na, Cl reabsoption increases K secretion

Parasympathetic Origin

salivary nucleus in medullaOutflow

CN VII & IX Transmitter

Ach Increased stimulation in response to conditioned reflexes (taste, smell) Decreased stimulation due to sleep, fear, dehydration

Stimulates - initiation & maintenance of secretion (protein poor, high k and HCO3) - contraction of myoepithelial cell - metabolic rate - blood flow - direct innervation of blood vessels

- growth

Sectioning of parasympathetic markedly decreases flow & leads to atrophy

Parasympathetic

Sympathetic

Originintermediolateral gray T1-T3

Transmitternorepinephrine

Stimulates - secretion (mostly enzymes)

- contraction of myoepithelial cell- metabolic rate

Sympathetic

Stimulates (cont)- growth

Sectioning of sympathetic nerves has minimal impact on secretion